1. Technical Field of the Invention
The present invention relates to a method of reducing the down time associated with replacing graphite components of a semiconductor fabrication unit.
2. Background of the Invention
Carbon/Graphite is employed extensively in Ion Implant systems due to its inertness, its favorable electrical and mechanical properties, its benign chemical footprint, and its relative low cost when compared with refractory metals. A wide range of graphite grades with nominally acceptable properties are readily available in the market. All of these grades, however, share some characteristics that are detrimental to the process of implanting species onto silicon wafers. Constant bombardment with charged particles wears graphite components, degrading their ability to control the ion beam and leading to instability. The products of this wear mechanism are particles of graphite that can impact wafer yields.
The processes by which graphite implant components are manufactured involve mechanical grinding and milling shapes from larger blocks. These processes define physical features by mechanically breaking covalent bonds and liberating particles of graphite. The majority of these particles are transported away from articles in process through vacuum removal; however, a portion of the material is impacted into the porosity of the ceramic substrate. Consequently, there is a need to provide particle removal in excess of that removal achieved by employing conventional vacuum for smaller semiconductor devices.
In addition to the creation of particulates, mechanical stress imparted at the surface leaves sub-surface cracking, leaving particles with lower bond energy than that of the bulk. These two phenomena are believed to be causal to the high rate of particle liberation, and subsequent glitching and low wafer yields, seen in the early lifetime of implant components.
Anecdotal evidence from wafer fabrication users and equipment OEMs suggests that particulation from graphite components in the Implant system follows a ‘bathtub’ curve, That is, the number of particles generated early in the life of the components is high, then drops off to a constant, and finally increases exponentially as components reach wear out.
As various graphite components of the Implant system wear out, the manufacturer must shut down the process in order to replace the worn out parts. In order to increase the reliability of the replacement components, the replacement graphite components must go through a “seasoning” process in which the Implant system is operated with the plasma chamber empty for several hours. This requirement further increases the down time associated with the cycle of failure and replacement of graphite components.
Therefore, it would be beneficial for a method wherein the “seasoning” step could be eliminated. Furthermore, it would be beneficial for a method to provide a graphite component that had an increased useful life, which would in turn reduce down time associated with replacement of said part.